Ship-to-Ship (STS) transfer operations involve transferring cargo between two seagoing vessels alongside each other, either while both are stationary or moving together.

This is a common practice for liquids like crude oil, gas, and chemicals, as well as for dry bulk cargo, and allows for cargo movement without using a port terminal. These are considered high-risk operations that require strict adherence to safety protocols, specialized equipment, and detailed planning to manage risks effectively.